Element x has two isotopes. the table gives information about these isotopes. x-63: has an atomic mass of 62.9296 amu and an abundance of 69.15% x-64: has an atomic mass of 64.9278 amu and an abundance of 30.85% the average atomic mass of element x is amu.

Answer : The average atomic mass of an element X is, 63.546 amu

Solution : Given,

Mass of isotope X-63 = 62.9296 amu

% abundance of isotope X-63 = 69.15% = 0.6915

Mass of isotope X-64 = 64.9278 amu

% abundance of isotope X-64 = 30.85% = 0.3085

Formula used for average atomic mass of an element X :

Therefore, the average atomic mass of an element X is, 63.546 amu

The idea is to sum up the product of atomic mass and abundance for each of the isotope- e.g. 62.9296 and 69.15% for X-63- to find the average of isotope atomic mass weighted regarding their abundance, which is by definition the relative atomic mass of the element.